Drug screening identifies tazarotene and bexarotene as therapeutic agents in multiple sulfatase deficiency

Multiple sulfatase deficiency (MSD, MIM #272200) results from pathogenic variants in the SUMF1 gene that impair proper function of the formylglycine-generating enzyme (FGE). FGE is essential for the posttranslational activation of cellular sulfatases. MSD patients display reduced or absent sulfatase activities and, as a result, clinical signs of single sulfatase disorders in a unique combination. Up to date therapeutic options for MSD are limited and mostly palliative. We performed a screen of FDA-approved drugs using immortalized MSD patient fibroblasts. Recovery of arylsulfatase A activity served as the primary readout. Subsequent analysis confirmed that treatment of primary MSD fibroblasts with tazarotene and bexarotene, two retinoids, led to a correction of MSD pathophysiology. Upon treatment, sulfatase activities increased in a dose- and time-dependent manner, reduced glycosaminoglycan content decreased and lysosomal position and size normalized. Treatment of MSD patient derived induced pluripotent stem cells (iPSC) differentiated into neuronal progenitor cells (NPC) resulted in a positive treatment response. Tazarotene and bexarotene act to ultimately increase the stability of FGE variants. The results lay the basis for future research on the development of a first therapeutic option for MSD patients.

Postnatal microcephaly and retinal involvement expand the phenotype of RPL10-related disorder

Hemizygous missense variants in the RPL10 gene encoding a ribosomal unit are responsible for an X-linked syndrome presenting with intellectual disability (ID), autism spectrum disorder, epilepsy, dysmorphic features, and multiple congenital anomalies. Among 15 individuals with RPL10-related disorder reported so far, only one patient had retinitis pigmentosa and microcephaly was observed in approximately half of the cases. By exome sequencing, three Italian and one Spanish male children, from three independent families, were found to carry the same hemizygous novel missense variant p.(Arg32Leu) in RPL10, inherited by their unaffected mother in all cases. The variant, not reported in gnomAD, is located in the 28S rRNA binding region, affecting an evolutionary conserved residue and predicted to disrupt the salt-bridge between Arg32 and Asp28. In addition to features consistent with RPL10-related disorder, all four boys had retinal degeneration and postnatal microcephaly. Pathogenic variants in genes responsible for inherited retinal degenerations were ruled out in all the probands. A novel missense RPL10 variant was detected in four probands with a recurrent phenotype including ID, dysmorphic features, progressive postnatal microcephaly, and retinal anomalies. The presented individuals suggest that retinopathy and postnatal microcephaly are clinical clues of RPL10-related disorder, and at least the retinal defect might be more specific for the p.(Arg32Leu) RPL10 variant, suggesting a specific genotype/phenotype correlation.

Expanding the phenotype of HNRNPU-related neurodevelopmental disorder with emphasis on seizure phenotype and review of literature

Pathogenic variants in heterogeneous nuclear ribonucleoprotein U (HNRNPU) results in a novel neurodevelopmental disorder recently delineated. Here, we report on 17 previously unpublished patients carrying HNRNPU pathogenic variants. All patients were found to harbor de novo loss-of-function variants except for one individual where the inheritance could not be determined, as a parent was unavailable for testing. All patients had seizures which started in early childhood, global developmental delay, intellectual disability, and dysmorphic features. In addition, hypotonia, behavioral abnormalities (such as autistic features, aggression, anxiety, and obsessive-compulsive behaviors), and cardiac (septal defects) and/or brain abnormalities (ventriculomegaly and corpus callosum thinning/agenesis) were frequently observed. We have noted four recurrent variants in the literature (c.1089G>A p.(Trp363*), c.706_707del p.(Glu236Thrfs*6), c.847_857del p.(Phe283Serfs*5), and c.1681dels p.(Gln561Serfs*45)).

Beclin-1-mediated activation of autophagy improves proximal and distal urea cycle disorders

Urea cycle disorders (UCD) are inherited defects in clearance of waste nitrogen with high morbidity and mortality. Novel and more effective therapies for UCD are needed. Studies in mice with constitutive activation of autophagy unravelled Beclin-1 as druggable candidate for therapy of hyperammonemia. Next, we investigated efficacy of cell-penetrating autophagy-inducing Tat-Beclin-1 (TB-1) peptide for therapy of the two most common UCD, namely ornithine transcarbamylase (OTC) and argininosuccinate lyase (ASL) deficiencies. TB-1 reduced urinary orotic acid and improved survival under protein-rich diet in spf-ash mice, a model of OTC deficiency (proximal UCD). In AslNeo/Neo mice, a model of ASL deficiency (distal UCD), TB-1 increased ureagenesis, reduced argininosuccinate, and improved survival. Moreover, it alleviated hepatocellular injury and decreased both cytoplasmic and nuclear glycogen accumulation in AslNeo/Neo mice. In conclusion, Beclin-1-dependent activation of autophagy improved biochemical and clinical phenotypes of proximal and distal defects of the urea cycle.

Activation of the c-Jun N-terminal kinase pathway aggravates proteotoxicity of hepatic mutant Z alpha1-antitrypsin

Alpha1-antitrypsin deficiency is a genetic disease that can affect both the lung and the liver. The vast majority of patients harbor a mutation in the serine protease inhibitor 1A (SERPINA1) gene leading to a single amino acid substitution that results in an unfolded protein that is prone to polymerization. Alpha1-antitrypsin defciency-related liver disease is therefore caused by a gain-of-function mechanism due to accumulation of the mutant Z alpha1-antitrypsin (ATZ) and is a key example of an disease mechanism induced by protein toxicity. Intracellular retention of ATZ triggers a complex injury cascade including apoptosis and other mechanisms, although several aspects of the disease pathogenesis are still unclear. We show that ATZ induces activation of c-Jun N-terminal kinase (JNK) and c-Jun and that genetic ablation of JNK1 or JNK2 decreased ATZ levels in vivo by reducing c-Jun-mediated SERPINA1 gene expression. JNK activation was confirmed in livers of patients homozygous for the Z allele, with severe liver disease requiring hepatic transplantation. Treatment of patient-derived induced pluripotent stem cell-hepatic cells with a JNK inhibitor reduced accumulation of ATZ.

CONCLUSION

These data reveal that JNK is a key pathway in the disease pathogenesis and add new therapeutic entry points for liver disease caused by ATZ. (Hepatology 2017;65:1865-1874).